1. Field of the Invention
The invention relates in general to a stopper assembly for use with a syringe and, more particularly, to a stopper assembly having low dead space and essentially zero reflux for use with a pre-filled syringe such as those used in flush applications. The invention also relates to a plunger rod and an attachment member adapted for attachment with a stopper assembly.
2. Description of Related Art
Pre-filled syringes, such as those used in flush applications, are typically filled with a saline solution and are used to flush catheters. Examples of pre-filled syringes are shown in U.S. Pat. Nos. 6,361,524 and 6,743,216, which are incorporated herein by reference and which are directed to syringe assemblies for flush applications. During use, the nurse or technician “bottoms out” the stopper in the syringe barrel at the end of the flushing procedure. The process of bottoming out the stopper in the barrel can cause a phenomenon known as reflux. Reflux is the reversal of fluid flow up through the catheter, usually due to the spring back of the stopper at the end of a flush injection. Reflux may occur when the stopper compresses to force out additional saline and subsequently springs back to shape, causing saline to be pulled back into the syringe. Reflux can also pull blood back into the catheter, clogging it. This phenomenon of reflux may be detrimental to the maintenance of the catheter line. Accordingly, it is desirable to reduce or eliminate reflux within the syringe.
Existing stopper designs typically include a constant diameter seal and a constant stopper-to-barrel interference to create a seal that will prevent fluid housed inside the barrel from leaking past the front seal of the stopper. The contact pressure of the seal is determined by the interference in these designs, and has to be sufficiently high such that the seal will not leak under the highest possible fluid pressure inside the barrel. The disadvantage of this traditional design is that higher contact pressures lead to higher static and dynamic frictional forces. Static friction is commonly referred to as “break loose” force. Additionally, existing stoppers typically include tip designs that are not self-centering. Because the tips are not self-centering, they do not form a positive seal with the inside back of the luer taper when subjected to axial forces.
Existing stopper designs have attempted to prevent the flow of fluid from the catheter back into the syringe by preventing spring back of the stopper which would create a vacuum to draw fluid back into the syringe. These designs, while effective in reducing reflux, do not consistently prevent all reflux from occurring. Further still, many of these designs include a significant amount of dead space volume. The ISO standard for dead space requirement for a 3 ml syringe is 70 μl, for a 5 ml syringe is 75 μl, and for a 10 ml syringe is 100 μl.